Aiming at a BreakthroughPresent Views and Future Prospects ofThin Film and Surface Physics
Kiyohiko UOZUMIChief, Thin Film and Surface Physics Division
Japan Society of Applied Physics
During my third year in university(1964), I investigated the temperature dependency of electrical conductivity in discontinuous metallic thin films as part ofstudent experiments. In this regard, conductance through film grains has a semiconductor-like temperature dependency having an activation energy inversely proportional to grainradius. At that time, Neugebauer and Webb had showed that thiscould be explained by an activated tunneling mechanism in which theenergy of charging film grains by a single electron is the activationenergy. The interesting aspects of this phenomenon prompted me toperform these experiments. In addition, Ivar Giaever, who received aNobel prize for measuring superconducting gaps by measurement oftunnel current between superconducting thin films, had observed aCoulomb blockade in conductance through Sn grains that form a thinoxidized film on a surface. Accordingly, the above phenomenon canalso be regarded as a classical phenomenon in what is called a “trivialeffect.” As you know, however, the measurement of conductancethrough literally one grain by a scanning tunneling microscope (STM)
and its explicit theoretical treatment came as a big surprise. Consequently, after treating tunnels between grains theoretically in a semiclassical manner and performing similar calculations and experiments,
I was somewhat disappointed to have been “beaten to the punch”
in this way. This so-called Coulomb blockade phenomenon also suggests that a staircase effect in tunnel-current characteristics can beobtained through multiple instances of grain charging by an electron,and that memory with storage retention can be achieved at room
temperature for sufficiently small grains.
The invention of the STM was a major breakthrough. With astructure featuring a sharpened probe tip that could pick up information from a local area on a surface, the STM takes on the formof a profile meter. Furthermore, as the tunnel current emitted fromone atom on the sharpened probe tip has atomic-order resolution,
the STM makes it possible to actually see individual atoms. A person
knowledgeable of experimental electronic circuits can easily create anSTM-related mechanism. For example, if information from the surfaceof the probe can be fed back as position data, the result is a scanningprobe microscope (SPM). Atoms and molecules can also be observed
as well as manipulated by an atomic force microscope (AFM), but
determining the makeup of a surface on a large scale requires highspeed scanning and/or parallel operation of many probes that caneach view a local section. In short, nano techniques having a twodimensional span as opposed to “pinpoint nano” are desirable. Without such techniques, we will not be able to take full advantage of theoutstanding features of nanotechnology to achieve novel devices forconveying information.
In relation to phenomena involved with material properties, thediscovery of materials exhibiting new properties can give birth tonew developments. Films of the carbon family such as diamond thinfilms and fullerene are examples of such materials, while the carbon
nanotube is a key example of how the discovery of a completely newmaterial can lead to explosive progress in research. It should be mentioned here that a joint program on such topics was formed among
concerned divisions at this autumn’s annual meeting of the JSAP.
Among researchers that have created diamond thin films, some noticed the existence of whisker-like matter, and the discovery of thisstructure should be commended. Configuring carbon nanotubes withsuch a structure would be optimal for STM and AFM probes, and astructure that could enclose various kinds of atoms and molecules
within a tube would be similar to a peapod type of atom/moleculesyringe. This structure is also expected to act as wiring material between man-made nanodots.
Thin film and surface physics covers a wide area of research. In
the field of ferroelectrics, for example, materials development and thedevelopment of film-formation techniques are actively being pursued
with the aim of achieving ferroelectric memory. Furthermore, thediscovery of new material properties is linked with the developmentof practical devices. While piezoelectric materials have been known
for some time, ZnO, which has come to be used as a surface filter, isgaining prominence as a newly evolving material. In the field of transparent conducting films, indium tin oxide (ITO) is a substance that has
been researched for some time, but research continues with the aimof improving its properties even further. These technologies include
many divisions of applied physics plus crystal engineering, appliedelectronic properties, and vacuum and surface techniques that act asa basis for creating devices. As such, they are becoming the foundation of modern industry including the development of new technologies for the fabrication of various types of thin films.
The International Conference on Atomically Controlled Surfaces,Interfaces and Nanostructures has been held by the Thin Film andSurface Physics Division every two years in Europe, the United States,
or Japan since its first meeting in Tokyo in 1991. The word “Nanostructures,” by the way, was added to the name of this conference atthe 1999 meeting held in France. The 7th International Conference
known as ACSIN-7 will be held in November 2003 at the New PublicHall in Nara, Japan. We are looking forward to strong participationfrom overseas researchers at this meeting. You can obtain more information at http://www.ele.eng.osaka-u.ac.jp/acsin7/.

JSAP International No.7 (January 2003)

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